1. Field of the Invention
The invention relates to chuck assemblies for tool bits and, more particularly, to a quick release chuck adapted to prevent undesired axial extraction of a tool bit such as a drill from the chuck assembly.
2. Description of the Prior Art
Tool bits include tools used for drilling, driving fastener devices such as screws, nuts and bolts, and other work elements requiring rotational motion. The American National Standards Institute has a specification for such tools known as ANSI B107.4-1982 which refers to driving and spindle ends for portable powered and hand held machines using the tool bits. Tool bits in accordance with the standard have a hexagonally configured shank with a circumferential groove formed into the shank. The circumferential groove has a flat, bottom portion disposed between two radiused shoulder portions. The standard reflects the long term and pervasive use of such tool bits and the large inventory of tools available.
It has long been recognized that the ability to quickly change tool bits in the spindle of a power source is an advantageous feature. Numerous examples exist in the art of quick release tool chucks. An example of one such quick release chuck apparatus is that described in U.S. Pat. No. 4,692,073. The quick release chuck disclosed therein includes a spring biased sleeve disposed on a spindle having an inclined cam surface disposed against a single ball. The ball in turn applies normal and tangential forces against a groove in the shank of the tool bit to hold the tool bit in a bore. The sleeve is urged into contact with the ball by a compression spring disposed between the spindle and the sleeve. A ring secured to the spindle limits the movement of the sleeve in one direction, and the compression spring and the spindle limit the movement of the sleeve in the opposite direction.
U.S. Pat. No. 4,692,073 addresses objectionable end play caused by the presence of the flat, bottomed portion of the circumferential groove in the tool bits. However, construction of devices taught by the patent require maintenance of extremely tight manufacturing standards with respect to the radius of the ball and both the radius of the radial bore it travels in and the radius of the radiused shoulders in the groove which it abuts against. The ramped sleeve which is used to apply normal and tangential forces to the ball can allow the ball to be forced out of the retaining position by a large outward axial force applied to the tool. A large outward axial force can occur, for example, where the tool bit is a drill bit being removed from a freshly drilled bore. Use of a single detent ball can also result in a nonconcentric orientation of the tool.